1. Field of the Invention
The present invention relates to a tool for machining by chip removal comprising a body of a hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride based material or high speed steel and a hard and wear resistant oxide designed to be used in machining of steel and stainless steel, preferably at high cutting speeds. The said coating is composed of one or more layers of which at least one layer is a textured physical vapour deposited (PVD) corundum phase alumina containing chromium (Al,Cr)2O3.
2. Description of the Related Art
Textured α-Al2O3 layers, produced with chemical vapour deposition (CVD) are disclosed in, e.g., EP 603144, EP 1528125, EP 1477581, EP 1655387, EP 659903, EP 738336, EP 1655388, EP 1655392, US 2007/104945, US 2004/202877.
EP 1479791 discloses a cutting tool composed of cemented carbide or cermet, and a hard coating; wherein the hard coating includes an α-Al2O3 layer formed by CVD, with the highest peak, measuring the inclination of the α-Al2O3 basal planes relative to the normal of the surface within a range of 0-10 degrees as determined by electron back scattering diffraction (EBSD).
EP 744473 discloses textured γ-Al2O3 layers produced by PVD.
U.S. Pat. No. 5,310,607 discloses a hard coating including (Al,Cr)2O3 crystals and a chromium content higher than 5 at % wherein the (Al,Cr)2O3 is a single crystal. The coating is deposited at a temperature lower than 900 C. The hard coating is deposited by a CVD or PVD process.
When machining steel with an alumina coated cemented carbide tool, the cutting edge is worn according to different wear mechanisms, such as chemical wear, abrasive wear, adhesive wear and by edge chipping caused by cracks formed along the cutting edge. The domination of any of the wear mechanisms is determined by the application, and is dependent on properties of the machined material, applied cutting parameters and the properties of the tool material. In general, it is very difficult to improve all tool properties simultaneously, and commercial cemented carbide grades have usually been optimised with respect to one or few of the above mentioned wear types, and have consequently been optimised for specific application areas. This can, for instance, be achieved by controlling the texture of the alumina layer.